The length and rhythm of games is definitely hurting a number of sports, football and baseball being the best examples.
I'm a huge advocate of shortening football games to 2-2.5 hours by reducing quarters to 12 minutes, not stopping the clock on incompletions, limiting replays (maybe going NFL route of 2 challenge flags/team), and reducing TV timeouts (adding on-field, on-uniform, and static on-screen advertising to replace that revenue).
The new AAF is coming soon, which I'm very interested to see. "Rules for the league include no kickoffs, required two-point conversions after touchdowns, limited replays and no television timeouts." CBS and CBS Sports will air games. I like what the AAF is thinking, making changes NFL and CFB ought to but are precluded from making by their own suffocating traditions and hubris.
Baseball is just a god-awfully slow sport. I used to love it in the 90s but other than a couple world series games, I can't watch but an at-bat or two. I don't even know how you make that more watchable without demolishing pitchers arms or yielding a ton of wild pitches.
Soccer has a great product and you know exactly when the game will end +/- 5 minutes. MLS seems to really be booming these days. ATL game I went to was a packed house and more rowdy than an FSU game. They've built a tremendous culture around their organization and I would assume other MLS teams have as well - if not ATL UTD is a great blueprint to follow.
For baseball and football, it's an 'evolve or die' situation. Perhaps not die but become a niche (baseball) or regional (football) sport over then next 20 years.
Basketball has a great product as well but needs to do a little soul searching around replays, foul-fiestas toward the end of close games, and teams tanking down the stretch.